In biological research, small scale cell culture is often conducted on the surface of microscope slide coverslips. Coverslips are readily available, easily cleaned and uniform. Coverslips are commonly made from glass and plastic. The coverslips are available as circles with diameters of 12 millimeters (mm) and 18 mm, squares with 18 mm, 22mm and 25 mm sides and rectangles dimensioned from 11 mm by 22 mm to 48 mm by 60 mm. When used for cell culture, the coverslips are generally cleaned, often coated with protein, dried and placed in a culture vessel having a flat bottom. The culture vessels used for these procedures are either Petri dishes, where several coverslips may be placed at one time, spaced apart from each other, or a multi-well plate where each coverslip is placed in an individual well.
A reference text entitled, Culturing Nerve Cells, G. Banker and K. Goslin, MIT Press, (1991) discusses the use of coverslips for cell culture. In the reference, the use of coverslips is reported in a "Protocol for Preparing Low-Density Hippocampal Cultures" on pages 255-259. The "protocol" reports that it is difficult to apply microscopic techniques to cells grown directly in plastic culture dishes. The "protocol" suggests plating hippocampal cells onto glass coverslips treated with a protein, polylysine, to enhance cell adhesion.
According to the "protocol," to conduct a cell mono-culture, i.e., growing only one type of cells, protein coated coverslips are placed flat on the bottom of a container, generally a Petri dish or a well of a multiwell plate, and a cell suspension in an aqueous medium is added to the container. The container with the coverslip and the suspension is incubated to develop a substantially confluent monolayer of the cells on the coverslip. For microscopic analysis of the cells or for further treatment of the cells, the coverslip with the monolayer of cells generally must be removed from the container with forceps. Since both the coverslip and the container bottoms are substantially flat, the aqueous medium often causes the coverslip to adhere strongly to the bottom of the container. Because of this adhesion, handling the coverslip with forceps often cracks the coverslip, disrupts the cells and may render the cells on the coverslip useless for further work.
When a cell co-culture is conducted, i.e., growing cells of a first type in close proximity to cells of a second type so that they interact chemically without direct contact, the coverslip and container technique also is useful. In the "protocol" from the reference Culturing Nerve Cells, the authors suggest applying small dots of wax to the edges of a coverslip prior to coating the coverslip with protein. To prepare a co-culture according to the "protocol," cells of a first type are cultured on the coverslip, on the side with the wax dots, following the mono-culture procedure to a confluent monolayer. The need to culture the first type cells on the side of the coverslip with the wax dots continues the possibility that some coverslips may crack in the handling necessary for the next step. Then, the coverslip with the first type cells is removed from its original container and placed in a second container with a confluent monolayer of cells of a second type cultured on its bottom surface so that the coverslip side having the first type cells faces the second type cells in the second container. In the placement of the coverslip in the second container, the wax dots support the coverslip with the first type of cells on the surface in close proximity to the cells of the second type. In this co-culture application using coverslips, the wax dots provide a separation between the coverslip and the container bottom. In addition to allowing the co-culture to proceed without direct contact between the cells, the wax dots allow the coverslip to be easily picked up and manipulated with forceps by substantially preventing adherence of the coverslip to the bottom of the container.
The addition of wax dots to a coverslip, while providing a separation between the coverslip and the container bottom, is time consuming and technique sensitive. Additionally, the wax dots are a potential source of contamination and may come off during handling. If a coverslip holder was available that would support a coverslip above the bottom of a vessel, the, efficiency and effectiveness of laboratory work in cell mono-culture and co-culture would be. enhanced. Such a holder is described below.